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Old 04-07-15, 02:40 PM   #1
dablack
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Default Just put on metal roof, rigid foam and spray foam

If you have seen some of my old threads you know that we are building our house. Most of the lumber came from my trees. I have a buddy with a sawmill so he cut all the framing and subfloor upstairs.

Well, we mostly finished electrical and plumbing rough in so I had the metal roof put on and the spray foam done.

For the metal roof, we went with galvalume r panel. I bought a bunch of used blue XPS. I had them put 2x4s horizontally spaced 4' apart. Then they put in two layers of the 3/4" foam sheets between the 2x4s. This gives me R7.5 above the roof deck.

For the spray foam, I paid for 3" of open cell foam but got 4" in most of the house. In some places, I got 5.5" (fill the cavity). Assuming 3.5", I have R13 in the walls and attic rafters. That puts me at R20.5 in the attic and right now have R13 in the walls.

The walls will get two layers of rigid on the outside as well. So, the whole house will be at least R20.5. For east texas, that is pretty good.

Austin









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Last edited by Daox; 04-07-15 at 03:52 PM..
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Old 04-07-15, 04:29 PM   #2
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For Texas that sounds very good! Nice job, and thanks for sharing with us.
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Old 04-09-15, 12:04 AM   #3
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Quote:
Originally Posted by dablack View Post
...The walls will get two layers of rigid on the outside as well. So, the whole house will be at least R20.5. For east texas, that is pretty good.
Yeah, it will sure help with the winter chill.

I did pretty much the same thing to my house, metal roof, rigid foam, etc.

One detail I wish I had included is a 1.5" or 2" air channel below the metal roof, and above the foam insulation structure, so that the house could self-ventilate air from vents in the eves, on up and out through some kind of ridge vent. As it is, my winter insulation is doing a really good job, but too much summer heat is making its way into my house.

By the way, what part of E. Texas are you in? I used to live in Nacogdoches, TX during my college days.

Best,

-AC
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Old 04-09-15, 09:02 AM   #4
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No vents in my eves or peak. All sealed inside and out.

Down here I'm not too worried about the chill. I'm just trying to block out heat. Usually during a sunny day, the upstairs gets hot even if it is just 65F outside. Now with the metal and rigid foam, it stays nice and cool up there. The internal spray foam made it even better.

Nacogdoches is just 30 minutes away. We are west of there in Rusk. I didn't go to school there but my school plays football against them now days. Small world.

Austin
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Old 04-09-15, 01:32 PM   #5
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...Small world...
Big Internet!

-AC
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Old 04-10-15, 03:26 AM   #6
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Looks great! You're way ahead of the curve as far as local construction. Its amazing how poor normal construction design is. I was in an attic yesterday,85F high outside measured 120-130F in the attic. This house was less than 10 years old, I blame the hipped roof with only a few gravity vents. I'm doing the same 'Texas Cool Roof" from your previous post. I believe you have some venting, between your metal and your rigid foam roof deck. My wife and friends went to SFA back in the day.
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Old 04-12-15, 09:53 AM   #7
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GTOjohn,

My roof is pretty close to the cool roof way of doing it. If I would have had more time and wasn't paying someone to do it, it would have been a little closer.

On the cool roof you have at least a 3/4" channel under the metal. My roof doesn't have that. All we did was put down horizontal 2x4s (so 1.5" proud of the roof deck) and then laid down two layers of 3/4" foam between the 2x4s. So the foam and surface of the 2x4s is flush. Then you attach the metal to the 2x4s. So, no vent to the peak. With the silver and the rigid foam, I think I'm ok. If it was a dark metal roof, I would for sure have the vent under the metal.

I'm planning on doing the siding the same way. With the siding, I'm going to put on vertical 2x4s and then put foam between them. Then attach the siding to the 2x4s. Not perfect but better than nothing.

Austin
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Old 04-12-15, 09:53 AM   #8
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Also, my sister was at SFA from 87 to 90 or 91.
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Old 04-12-15, 10:23 PM   #9
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I remember wearing a T shirt during a visit to that exact area last January. During the summer, the atmosphere is so thick with heat and humidity you could almost swim in it. Got bunches of relatives there.
I think you chose the right insulation and roof for that climate too.
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Old 04-13-15, 08:27 AM   #10
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Getting a little closer to siding.

I have a bunch of 8.25" wide hardie boards coming. So I was checking the spacing on attaching them and hardie says they want 2' OC. That is much closer than I was thinking. I really don't want to rip my foam into 2' wide strips.

So, then I started googling putting hardie on top of rigid foam. Sure enough, they have a paper out there sayings 1" of foam and under, you can just nail through the foam. Anything over 1" and they want you to put on lathe and nail to that. We are going to put on two layers of 3/4" foam, so that makes 1.5" of foam. I really don't want to do lathe under my siding. I would love to have a rain screen but I'm running out of time and money. I'm thinking about attaching it 16" OC through the foam. With the right sized fastener, I think it will be fine. Hardie says that 7/16" OSB will hold it but I'm going to try and hit the studs (which are also 16" OC). I will post pictures as I go.

Austin

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